Abstract
ABSTRACTThere is a growing concern over the food safety issue related to increased incidence of cooking oil adulteration with recycled cooking oil (RCO). The objective of this study was to detect fresh palm olein (FPO) adulteration with RCO using fatty acid composition (FAC) and Fourier-transform infrared spectroscopy (FTIR) spectral analyses combined with chemometrics. RCO prepared in the laboratory was mixed with FPO in the proportion ranged from 1% to 50% (v/v) to obtain the adulterated oil samples (AO). FACs for FPO, RCO, and AO were determined using gas chromatography equipped with a flame ionization detector (GC-FID). The compositions of most fatty acids in RCO lied within the normal ranges of Codex standard, except for C8:0, C10:0, C11:0, C15:0, trans C18:1, and polyunsaturated fatty acids (PUFAs), C20:5. PUFAs showed a consistent decreasing trend with increasing magnitude of change with respect to increasing adulteration level and thus might be a good indicator for detecting FPO adulteration with RCO. The evaluation parameters (coefficient of determination, root mean standard error) of the FTIR-partial least square (PLS) model of palm oil adulteration with recycled oil are R2 = 0.995 and 3.25, respectively. For FTIR spectral analysis, the distinct variations in spectral regions and aberrations in characteristic bands between FPO and RCO were observed. The optimized PLS calibration model developed from normal spectral of the combined region at 3602–3398, 3016–2642, and 1845–650 cm−1 overpredict the adulteration level. On the other hand, the discriminant analysis classification model was able to classify the FPO and AO into two distinct groups. Improvement of the principles of combined techniques in authenticating AO from fresh oil is beneficial as a guideline to detect adulteration in cooking oil.
Highlights
Used cooking oil refers to animal- or plant-based fats and oils, which have been used for food preparation processes
A further refinement on the principles and concepts of both techniques (FAC analysis and Fourier-transform infrared spectroscopy (FTIR) spectral analysis combined with chemometrics) is needed for a more convincing outcome to resolve the issue of fresh palm olein (FPO) adulteration with recycled cooking oil (RCO)
Several noticeable alterations in fatty acid composition (FAC) of RCO was observed when compared to FPO, which included (i) the appearance of short-chain fatty acids (C8:0 and C10:0), trans fatty acids, and other fatty acids not found in FPO (C11:0 and C20:5); (ii) the significant increase in Odd-chain fatty acids (OCFAs); (iii) significant increase in monounsaturated fatty acids (MUFAs); and (iv) insignificant decrease in polyunsaturated fatty acids (PUFAs)
Summary
Used cooking oil refers to animal- or plant-based fats and oils, which have been used for food preparation processes. Fresh cooking oil adulteration with RCO has been prevalent in China in 2011,[6] before it was reported in other countries, such as Taiwan.[7] Neglecting this issue would further spread the problem, putting consumers at high risk as they could be the victims of the fresh cooking oil adulteration with RCO that happened anywhere. It may provoke the concern on ‘halal’ issue as well.[1]
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